This invention relates to a cambering apparatus provided with variable dies, in which the camber profile to be imparted thereby to leaf spring blanks can be changed in a short time.
Suspension systems consisting of a plurality of leaves 10 which are laminated and bound as shown in FIG. 13 are suitably employed in land transportation vehicles such as railway cars and trucks. Each of the leaves 10 can be prepared, for example; after formation of an eye at one end portion or each end portion of a rolled plate blank having a predetermined thickness or a taper at the other end portion thereof, by subjecting the thus processed blank, which is heated entirely, to a cambering treatment so as to be provided with a predetermined camber. The camber to be imparted to the blank varies depending on the application and load stress to be applied thereto: a type in which the camber angle gradually diminishes or increases from the center toward each end, a type in which the middle portion has no camber, etc.
FIG. 14 shows one example of prior art cambering apparatus 12 for imparting a camber to a leaf spring blank 10. The cambering apparatus 12 basically consists of an upper die 14 and a lower die 16. The upper die 14 is a female mold, whereas the lower die 16 is a male mold. A straight leaf spring blank 10 heated to a hot working temperature is placed between the upper die 14 and the lower die 16, and then the upper die 14 is forced to approach the lower die 16 to impart a camber conforming to the profile of these dies 14,16.
The mode of manufacturing leaf springs 10 includes:
(1) Group production mode in which leaves 10 of the same shape and the same specifications are continuously manufactured by the group lot; and PA1 (2) Family production mode in which a main leaf 10 and the other leaves 10 constituting a suspension system are manufactured by the family lot. A suitable production mode is selected by users .depending on the application and other factors. In the group production mode, after a predetermined large lot number of leaves 10 of the same shape are manufactured, the upper die 14 and the lower die 16 in the cambering apparatus 12 are changed only when a different camber profile is to be imparted in accordance with an order change. It generally takes much time for the change-over of molds, which is a main factor of notably reducing efficiency in cambering leaf spring blanks 10. Particularly today when small lot production is prevalent, countermeasures must be taken for possible frequent order changes, and it is becoming extremely important to minimize the mold change-over time in the laminated spring manufacturing industry.
Meanwhile, in the family production mode, each time a leaf spring blank 10 is cambered, the upper die 14 and the lower die 16 must be changed, since the camber to be imparted to each leaf spring blank is slightly different. Accordingly, this mode also suffers a disadvantage in that it requires extremely intricate procedures and also a considerable loss time. In this regard, the conventional cambering apparatuses are far from satisfaction for meeting the demand of the industry. Further, various kinds of upper dies 14 and lower dies 16 corresponding to the different camber profiles are necessary in the group production mode and the family production mode, leading to production cost elevation. Moreover, inconveniences can be pointed out that the upper dies 14 and lower dies 16 must be stored separately, so that a wide space is required for the storage of these dies and that stock management becomes troublesome. Besides, if the upper dies 14 and the lower dies 16 are used over a long period, it sometimes happens that the molding surfaces thereof wear with time and are deformed to be unable to impart accurate camber to leaf spring blanks 10. In such cases, while the dies 14,16 must be repaired or replaced with new ones, the procedures of repairing or replacing the dies take much time, causing reduction in the production efficiency.
Under such circumstances, the present applicant previously filed an application of an invention entitled "Leaf spring blank cambering method and apparatus therefor" as a proposal for coping with the problems described above. In the cambering apparatus according to this previous application, a holder is ascendably disposed on a base frame constituting the main body of the apparatus, and a multiplicity of shaping fingers are disposed on the holder to be movable in the vertical direction. The positions of the respective shaping fingers are adapted to be adjusted via corresponding servo motors and screw shafts provided on the holder so that a predetermined camber profile may be formed as a whole by the free ends of the group of shaping fingers. According to the cambering apparatus of such constitution, when the camber profile to be imparted to leaf spring blanks is changed in accordance with an order change, the positions of the plurality of shaping fingers may only be adjusted, and thus the time required for the set-up change can be reduced. Besides, there is no need of providing various shapes of moldes, leading to easy stock management and eliminating repair or replacement of dies.
However, this type of cambering apparatus also involves problems in that it is not only expensive but also the mechanism thereof is complicated, because the servo motors for adjusting the positions of the shaping fingers are disposed corresponding to the number of shaping fingers. Further, while a great load is applied to the shaping fingers when a leaf spring blank is to be cambered by the shaping fingers, the screw shafts for adjusting the positions of the fingers are also subjected to such load and are liable to be damaged.